1. Field of the Invention
The present invention relates to an optical coupling device or optocoupler and, more particularly, the present invention relates to an optical coupling device having a high coupling factor which is both physically small and which may also be reliably manufactured.
2. Description of the Related Art
Optical coupling devices or optocouplers are generally known in the art and are used where it is desired to maintain electrical isolation between two circuits. Optical coupling and the resultant electrical isolation allows reaction free and potential-free signal transmission between two circuits and decreases noise in the signals transmitted between the circuits.
Optical couplers typically are comprised of a light-emitting semiconductor device which operates as the optical transmitter and a light-detecting semiconductor device which functions as the optical receiver. The optical transmitter and receiver are usually integrated into a single housing and are electrically isolated from each other. In a typical optical coupling device, a light-emitting diode (LED or IRED) that emits light in the visible or infrared wavelength range is employed as the optical transmitter and a photodiode or photo-transistor operates as the optical receiver. A GaAs IRED combined with a Si phototransistor is a standard combination as these devices may be easily tuned to each other. This is due to the fact that the maximum emission of the gallium arsenide diode nearly coincides with the highest spectral sensitivity of the silicon transistor. Optocouplers provide numerous advantages over mechanical relays, including, the elimination of all moving parts, long service life, small size, compatibility with semiconductor circuits and, most significantly, their high switching frequency.
Various optical coupling devices are known in the art. One such optical coupler is disclosed in German patent application No. 37 13 067 wherein a transmitter chip and a receiver chip are firmly joined to one another via an optical coupling medium. The coupling medium acts as an insulating transparent intermediate layer. The transmitter chip, coupling medium and receiver chip are directly connected to one another and are in fact layered on top of one another.
German Patent Application No. 36 33 251 discloses an optocoupler wherein an optical transmitter chip and an optical receiver chip are directly connected to one another via a coupling medium comprised of a transparent adhesive or glass solder. Fiber glass sections or glass balls can be added to this coupling medium as transparent spacer particles.